module RSpec::Its

# File lib/rspec/its.rb, line 128
def its(attribute, *options, &block)
  its_caller = caller.grep_v(%r{/lib/rspec/its})

  describe(attribute.to_s, caller: its_caller) do
    let(:__its_subject) { RSpec::Its::Subject.for(attribute, subject) }

    def is_expected
      expect(__its_subject)
    end
    alias_method :are_expected, :is_expected

    def will(matcher = nil, message = nil)
      raise ArgumentError, "`will` only supports block expectations" unless matcher.supports_block_expectations?

      expect { __its_subject }.to matcher, message
    end

    def will_not(matcher = nil, message = nil)
      raise ArgumentError, "`will_not` only supports block expectations" unless matcher.supports_block_expectations?

      expect { __its_subject }.to_not matcher, message
    end

    def should(matcher = nil, message = nil)
      RSpec::Expectations::PositiveExpectationHandler.handle_matcher(__its_subject, matcher, message)
    end

    def should_not(matcher = nil, message = nil)
      RSpec::Expectations::NegativeExpectationHandler.handle_matcher(__its_subject, matcher, message)
    end

    options << {} unless options.last.is_a?(Hash)
    options.last.merge!(caller: its_caller)

    __its_example(nil, *options, &block)
  end
end

Creates a nested example group named by the submitted ‘attribute`, and then generates an example using the submitted block.

@example

# This ...
RSpec.describe Array do
  its(:size) { is_expected.to eq(0) }
end

# ... generates the same runtime structure as this:
RSpec.describe Array do
  describe "size" do
    it "is_expected.to eq(0)" do
      expect(subject.size).to eq(0)
    end
  end
end

The attribute can be a ‘Symbol` or a `String`. Given a `String` with dots, the result is as though you concatenated that `String` onto the subject in an expression.

@example

RSpec.describe Person do
  subject(:person) do
    Person.new.tap do |person|
      person.phone_numbers << "555-1212"
    end
  end

  its("phone_numbers.first") { is_expected.to eq("555-1212") }
end

When the subject is a ‘Hash`, you can refer to the Hash keys by specifying a `Symbol` or `String` in an array.

@example

RSpec.describe "a configuration Hash" do
  subject do
    { :max_users => 3,
      'admin' => :all_permissions.
      'john_doe' => {:permissions => [:read, :write]}}
  end

  its([:max_users]) { is_expected.to eq(3) }
  its(['admin']) { is_expected.to eq(:all_permissions) }
  its(['john_doe', :permissions]) { are_expected.to eq([:read, :write]) }

  # You can still access its regular methods this way:
  its(:keys) { is_expected.to include(:max_users) }
  its(:count) { is_expected.to eq(2) }
end

With an implicit subject, ‘should` can be used as an alternative to `is_expected` (e.g. for one-liner use). An `are_expected` alias is also supplied.

@example

RSpec.describe Array do
  its(:size) { should eq(0) }
end

With an implicit subject, ‘will` can be used as an alternative to `expect { subject.attribute }.to matcher` (e.g. for one-liner use).

@example

RSpec.describe Array do
  its(:foo) { will raise_error(NoMethodError) }
end

With an implicit subject, ‘will_not` can be used as an alternative to `expect { subject.attribute }.to_not matcher` (e.g. for one-liner use).

@example

RSpec.describe Array do
  its(:size) { will_not raise_error }
end

You can pass more than one argument on the ‘its` block to add some metadata to the generated example

@example

# This ...
RSpec.describe Array do
  its(:size, :focus) { is_expected.to eq(0) }
end

# ... generates the same runtime structure as this:
RSpec.describe Array do
  describe "size" do
    it "is expected to eq(0)", :focus do
      expect(subject.size).to eq(0)
    end
  end
end

Note that this method does not modify ‘subject` in any way, so if you refer to `subject` in `let` or `before` blocks, you’re still referring to the outer subject.

@example

RSpec.describe Person do
  subject { Person.new }

  before { subject.age = 25 }

  its(:age) { is_expected.to eq(25) }
end